Trapping area creating method, trapping area creating apparatus, and trapping area creating program storage medium

ABSTRACT

A trapping area creating method in which an image represented in form of a combination of polygons is divided into a plurality of image areas by a straight line passing through vertexes of the polygons. The propriety of trapping is decided for each pair of image areas adjacent to one another in at least one direction of two predetermined directions, with respect to the plurality of image areas wherein the image is divided. A band-shaped trapping area extending along a boundary of two image areas constituting a pair of image areas decided as being suitable for a trapping is created.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a trapping area creating method ofcreating a band-shaped trapping area extending along the coloridentification boundary of an image, a trapping area creating apparatusfor creating a trapping area, a trapping area creating program forcausing a computer to execute the trapping area creating method when thetrapping area creating program is incorporated into the computer, and atrapping area creating program storage medium storing the trapping areacreating program.

2. Description of the Related Art

Generally, there is known a method of creating an image by amulticolored printing using a plurality of machine plates associatedwith a plurality of primary colors. In the event that on an imagecreated by such a multicolored printing there is a color identificationboundary in which colors near two primary colors are close to oneanother, it often brings about a blank space on the color identificationboundary owing to misregistration among a plurality of machine plates.In view of the foregoing, hitherto, there is performed a trapping ofcompensating for misregistration between machine plates by means ofedging one or both of two color areas contacting with each other at acolor identification boundary in which colors near two primary colorsare close to one another, at a band-shaped trapping area along the coloridentification boundary.

Recently, as a computer technology advances, it often happens thatediting of an image created by a multicolored printing is performed on acomputer. In this case, it is troublesome for editors to severallycreate the trapping area. Accordingly, there is desired a trapping areacreating program for automatically creating a trapping area from imagedata.

As a method of creating trapping area by such a trapping area creatingprogram, there is proposed, for example, a creating method in which animage is divided into a large number of small areas as a lattice,existence as to a color identification boundary is decided for eachsmall area, and the small areas associated with the color identificationboundary are coupled with one another to create a band-shaped trappingarea.

In order to create a band-shaped trapping area, it is necessary that animage be divided into a sufficiently large number of small areas.However, dividing the image into so large number of small areas causesan amount of computation to be enormous. This involves a problem that acreation of the trapping area is slow down.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a trapping area creating method capable of creating a trappingarea at high speed, a trapping area creating apparatus for creating atrapping area at high speed in accordance with such a trapping areacreating method, a trapping area creating program for causing a computerto execute the trapping area creating method when the trapping areacreating program is incorporated into the computer, and a trapping areacreating program storage medium storing the trapping area creatingprogram.

To achieve the above-mentioned object, the present invention provides atrapping area creating method comprising:

a division step of dividing an image represented in form of acombination of polygons to which colors are applied, into a plurality ofimage areas by a straight line passing through vertexes of the polygons;

a decision step of deciding a propriety of trapping for each pair ofimage areas adjacent to one another in at least one direction ofpredetermined two directions, with respect to the plurality of imageareas wherein the image is divided; and

a trapping area creating step of creating a band-shaped trapping areaextending along a boundary of two image areas constituting a pair ofimage areas decided as being suitable for a trapping in said decisionstep.

It is acceptable that the trapping area creating method according to thepresent invention includes, as an occasion arises, other than saiddivision step, a step of dividing the image by a straight line passingthrough an intersection of the sides constituting the polygon.

According to the trapping area creating method of the present invention,it is possible to create a trapping area even if the number of divisionsfor the image in the division step is kept on not many. Accordingly itis possible to create the trapping area at high speed with a computerand the like.

In the trapping area creating method according to the present inventionas mentioned above, it is preferable that said division step divides theimage using, as said straight line, straight lines extending in samedirections as said predetermined two directions passing through thevertexes of the polygon, and sides of the polygon.

Here, it is acceptable that the division step is one in which all thesides and the straight lines as mentioned above are used unconditionallyor alternatively another one in which those elements are optionallyselected.

According to the preferable trapping area creating method as mentionedabove, a direction of the straight line used for a division of the imageis contrived. Thus, it is possible to reduce the number of times ofdeciding propriety of trapping. As a result, it is possible to createthe trapping area at high speed.

In the trapping area creating method according to the present inventionas mentioned above, it is an aspect that said decision step typicallyadopts, as said predetermined two directions, an upper and lowerdirection and a right and left direction of the image.

In the trapping area creating method according to the present inventionas mentioned above, it is preferable that said decision step decides thepropriety of trapping in accordance with a difference between colors oftwo image areas constituting said pair of image areas. Decision of thepropriety of trapping can be performed readily and at high speed.

Further, in the trapping area creating method according to the presentinvention as mentioned above, it is preferable that said trapping areacreating step creates, as said trapping area, an area interposed betweena line constituting said boundary and a line obtained when said line(first occurring) is subjected to a parallel translation. Such an areacan be created readily and at high speed.

To achieve the above-mentioned object, the present invention provides atrapping area creating apparatus creating a trapping area in accordancewith a trapping area creating method comprising:

a division step of dividing an image represented in form of acombination of polygons to which colors are applied, into a plurality ofimage areas by a straight line passing through vertexes of the polygons;

a decision step of deciding a propriety of trapping for each pair ofimage areas adjacent to one another in at least one direction ofpredetermined two directions, with respect to the plurality of imageareas wherein the image is divided; and

a trapping area creating step of creating a band-shaped trapping areaextending along a boundary of two image areas constituting a pair ofimage areas decided as being suitable for a trapping in said decisionstep.

To achieve the above-mentioned object, the present invention provides atrapping area creating program, which causes a computer to execute atrapping area creating method comprising:

a division step of dividing an image represented in form of acombination of polygons to which colors are applied, into a plurality ofimage areas by a straight line passing through vertexes of the polygons;

a decision step of deciding a propriety of trapping for each pair ofimage areas adjacent to one another in at least one direction ofpredetermined two directions, with respect to the plurality of imageareas wherein the image is divided; and

a trapping area creating step of creating a band-shaped trapping areaextending along a boundary of two image areas constituting a pair ofimage areas decided as being suitable for a trapping in said decisionstep,

when said trapping area creating program is incorporated into saidcomputer.

To achieve the above-mentioned object, the present invention provides atrapping area creating program storage medium storing a trapping areacreating program, which causes a computer to execute a trapping areacreating method comprising:

a division step of dividing an image represented in form of acombination of polygons to which colors are applied, into a plurality ofimage areas by a straight line passing through vertexes of the polygons;

a decision step of deciding a propriety of trapping for each pair ofimage areas adjacent to one another in at least one direction ofpredetermined two directions, with respect to the plurality of imageareas wherein the image is divided; and

a trapping area creating step of creating a band-shaped trapping areaextending along a boundary of two image areas constituting a pair ofimage areas decided as being suitable for a trapping in said decisionstep,

when said trapping area creating program is incorporated into saidcomputer.

Incidentally, with respect to the trapping area creating apparatus ofthe present invention and the trapping area creating program of thepresent invention, only the basic embodiments are shown. However, thisis to do so in order to avoid the redundancy, and it is noted that thetrapping area creating apparatus of the present invention and thetrapping area creating program of the invention include not only thebasic embodiments, but also a various types of embodiments of thetrapping area creating apparatus and the trapping area creating programcorresponding to the above-mentioned trapping area creating method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart useful for understanding a trapping area creatingmethod according to an embodiment of the present invention.

FIG. 2 is a view showing an example of a component constituting animage.

FIG. 3 is an explanatory view for a segment resolution.

FIG. 4 is a view showing an example of a coordinate tree.

FIG. 5 is a view showing a segment resolution of a triangular componentshown in FIG. 2.

FIG. 6 is a view showing a coordinate tree of a triangular componentshown in FIG. 2.

FIG. 7 is a view showing a first step of the procedure in whichcoordinate trees are merged together.

FIG. 8 is a view showing a second step of the procedure in whichcoordinate trees are merged together.

FIG. 9 is a view showing a third step of the procedure in whichcoordinate trees are merged together.

FIG. 10 is a view showing a fourth step of the procedure in whichcoordinate trees are merged together.

FIG. 11 is a view showing a fifth step of the procedure in whichcoordinate trees are merged together.

FIG. 12 is a view showing a sixth step of the procedure in whichcoordinate trees are merged together.

FIG. 13 is a view showing a seventh step of the procedure in whichcoordinate trees are merged together.

FIG. 14 is a view showing a final step of the procedure in whichcoordinate trees are merged together.

FIG. 15 is a view showing area data generated from coordinate trees.

FIG. 16 is a view showing a divided image.

FIG. 17 is a view showing an image in which an area is divided.

FIG. 18 is a view showing a created trapping area.

FIG. 19 is a view showing a state that trapping areas are created on allthe area pairs shown in Table 4.

FIG. 20 is a view showing a first step of the procedure in which anintegrated trapping area is created.

FIG. 21 is a view showing a second step of the procedure in which anintegrated trapping area is created.

FIG. 22 is a view showing a third step of the procedure in which anintegrated trapping area is created.

FIG. 23 is a view showing a final step of the procedure in which anintegrated trapping area is created.

FIG. 24 is a perspective view of a trapping area creating apparatusaccording to an embodiment of the present invention.

FIG. 25 is a hardware structural view of a trapping area creatingapparatus according to an embodiment of the present invention.

FIG. 26 is a view showing an embodiment of a trapping area creatingprogram and a trapping area creating program storage medium of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothe accompanying drawings.

In the following explanation, the following image data and the like arepremised. That is, image data representative of an image is constructedin form of an assembly of component data, which are indicative ofcolored polygon. A figure constructed by a curve such as a circle isapproximately expressed by a polygon. Hereinafter, it happens that apolygon represented by the component data is referred to as “component”.

A plurality of polygons represented by a plurality of component dataconstituting the image data is involved in a relationship of the upperand lower sides. In a case where an “upper” of polygon is overlappedwith a “lower” of polygon, an external form and a color of the “upper”of polygon take priority. The component data includes coordinates of thevertexes constituting a polygon.

This type of image data has been utilized in various fields.

FIG. 1 is a flowchart useful for understanding a trapping area creatingmethod according to an embodiment of the present invention.

Of this flowchart, step 01 to step 11, which will be described later,constitute an example of a division step referred to in the presentinvention.

Further, of this flowchart, step 13, which will be described later,corresponds to an example of a decision step referred to in the presentinvention.

Furthermore, of this flowchart, step 14 to step 17, which will bedescribed later, constitute an example of a trapping area creating stepreferred to in the present invention.

Hereinafter, this flowchart will be explained in conjunction with theaccompanying drawings.

First, component data, which are objects for creation of coordinatestrees as will be described latter, are derived one by one from anassembly of component data constituting image data (a step 01 in FIG.1). Here, the component data are sequentially derived from the “lower”side in accordance with the above-mentioned relationship of the upperand lower sides, which is applied to the component data constitutingimage data.

FIG. 2 is a view showing an example of a component constituting animage.

An image shown in FIG. 2 consists of a rectangular component to whichmagenta is applied, and a triangular component to which cyan is applied.The rectangular component is the “lower” side, and the triangularcomponent is the “upper” side. Accordingly, first, the rectangularcomponent is derived, and then the triangular component is derived. Acomponent number for identifying a component is applied to each of thecomponents. Here, the component number “101” is applied to therectangular component, and the component number “102” is applied to thetriangular component.

Coordinates of four vertexes A1, A2, A3 and A4, which constitute therectangle, are expressed by (xa1, ya1), (xa1, ya2), (xa2, ya2) and (xa2,ya1), respectively. Coordinates of three vertexes B1, B2 and B3, whichconstitute the triangle, are expressed by (xb1, ya1), (xb2, yb2) and(xb3, yb2), respectively. It is noted that an X-coordinate value islarger with farther going toward the right of FIG. 2, and anY-coordinate value is larger with farther going downwards. Paths of thecomponents are subjected to a segment resolution in accordance withthose coordinate values (a step S02 in FIG. 1).

FIG. 3 is an explanatory view for a segment resolution.

FIG. 3 shows a segment resolution of the rectangular component shown inFIG. 2.

The segments constituting the component are determined in accordancewith the coordinate values of the vertexes including the component data.Those segments are classified into a horizontal line in which theY-coordinate values at both the edges are equal to one another, and anupper and lower line in which the Y-coordinate values at both the edgesare mutually different.

In FIG. 3, in order to distinguish the upper and lower line and thehorizontal line, a white circle and a black dot are applied to both theends of a upper and lower line 202, respectively, and four-sided figuresare applied to both the ends of a horizontal line 201, respectively.With respect to a component constituted of three or more upper and lowerlines 202, it is assumed that a supplement of the horizontal line and adivision of the upper and lower line are suitably performed, and thecomponent constituted of three or more upper and lower lines 202 isconverted into an assembly of components each having two upper and lowerlines.

With respect to the respective upper and lower line determined inaccordance with such a segment resolution, an upper end point and alower end point are extracted, and a coordinate tree, as will bedescribed latter, is created for each component in accordance with theextracted upper end point and lower end point (a step S03).

The black dot applied to the upper and lower lines 202 shown in FIG. 3denotes an upper end point 203, and the white circle denotes a lower endpoint 204. As described above, since the coordinates of four vertexesA1, A2, A3 and A4, which constitute the rectangle, are expressed by(xa1, ya1), (xa1, ya2), (xa2, ya2) and (xa2, ya1), respectively,coordinates of two upper end points 203 are expressed by (xa1, ya1) and(xa2, ya1), respectively, and coordinates of two lower end points 203are expressed by (xa1, ya2) and (xa2, ya2), respectively.

FIG. 4 is a view showing an example of a coordinate tree.

A coordinate tree 300 shown in FIG. 4 denotes the rectangular componentshown in FIG. 2.

The coordinate tree 300 consists of a trunk 302 in which Y-coordinatevalues 301 range, and branches 304 in which X-coordinate values 303associated with the Y-coordinate values 301 range. The Y-coordinatevalues 301 ranging to the trunk 302 and the X-coordinate values 303ranging to the branches 304 are sorted in the order of arrows. Appendedto each of the branches 304 are upper and lower sides data 305 fordistinguishing the upper side point from the lower side point, and acomponent number 306 of a component represented by the coordinate tree300. A pair of X-coordinate values 303 between the upper side pointsranging to one branch 304, or a pair of X-coordinate values 303 betweenthe lower side points ranging to one branch 304 denotes a horizontalline. And, a pair of X-coordinate value 303, to which the upper andlower sides data 305 representative of the upper side point is appended,and X-coordinate value 303 existing on a branch different from the firstoccurring coordinate value, to which the upper and lower sides data 305representative of the lower side point is appended, denotes a upper andlower line.

In a similar fashion to the procedures explained referring to FIGS. 3and 4, the triangular component shown in FIG. 2 is also subjected to asegment resolution so that a coordinate tree of the triangular componentis created.

FIG. 5 is a view showing a segment resolution of a triangular componentshown in FIG. 2. FIG. 6 is a view showing a coordinate tree of atriangular component shown in FIG. 2.

FIG. 5 shows a state in which the triangular component shown in FIG. 2is subjected to a segment resolution into one horizontal line 201 andtwo upper and lower lines 202. Those two upper and lower lines 202 forma vertex angle of a triangle. Coordinates of the upper side points 203of two the upper and lower lines 202 are expressed by (xb1, yb1). Thus,of the branches 311 of the coordinate tree 310 shown in FIG. 6, thebranches, in which the same X-coordinate values xb1 are ranged, denote ahorizontal line where the length is “0”.

When the step S01 to the step 03 in FIG. 1 is repeated so thatcoordinate trees of two or more components are created, the coordinatetrees are merged together (a step S04 in FIG. 1).

FIG. 7 to FIG. 14 are views each showing the procedure in whichcoordinate trees are merged together.

Hereinafter, there will be explained, a procedure that a coordinate tree310 shown in FIG. 6 is merged into the coordinate tree 300 shown in FIG.4, referring to FIG. 7 to FIG. 14.

First, as shown in FIG. 7, Y-coordinate values shown in the trunk of thecoordinate tree 310 shown in FIG. 6 are incorporated into the trunk 302of the coordinate tree 300 shown in FIG. 4. Here, by way of an example,there is shown a procedure that the Y-coordinate value yb1 isincorporated into the trunk 302. Since the Y-coordinate value yb1 is avalue between the Y-coordinate value ya1 and the Y-coordinate value ya2,the Y-coordinate value yb1 is supplemented between the Y-coordinatevalue ya1 and the Y-coordinate value ya2.

Next, as shown in FIG. 8, there is retrieved a pair of X-coordinatevalues indicative of upper and lower line exceeding the Y-coordinatevalue yb1. In FIG. 8, there is detected two pairs 320 of X-coordinatevalues each indicative of such upper and lower line. And as shown inFIG. 9, there are determined intersection points C1 and C2 of thehorizontal line having the Y-coordinate value yb1 and the detected upperand lower lines. And a new set of the lower side point 204 and the upperside point 203 is provided at the same positions as the intersectionpoints C1 and C2.

As shown in FIG. 10, four X-coordinate values xa1, xa1, xa2 and xa2corresponding to the newly provided lower side points and the upper sidepoints are added to the coordinate tree in form of a branch to theY-coordinate value yb1. As a result, as mentioned above, an image isdivided by the horizontal line coupling between the newly provided upperside points and the horizontal line coupling between the newly providedlower side points.

Further, as shown in FIG. 11, two X-coordinate values xb1 and xb1corresponding to the Y-coordinate value yb1 are extracted from thecoordinate tree 310 shown in FIG. 6 and are supplemented to thecoordinate tree 310 in FIG. 11. But, component numbers appended to thetwo X-coordinate values xb1 and xb1 thus supplemented are “102”, and aredifferent from the component numbers appended to other X-coordinatevalues shown in FIG. 11. That is, the supplemented two X-coordinatevalues xb₁ and xb₁ are supplemented in form of coordinate values ofvertexes constituting the component of the number “102”.

Thereafter, as shown in FIG. 12, X-coordinate values of branches to theY-coordinate value yb1 are sorted. And as shown in FIG. 13, X-coordinatevalues xb1 and xb1, which are the same as the X-coordinate values xb1and xb1 supplemented in FIG. 11, are further supplemented. The componentnumber appended to the supplemented two X-coordinate values xb1 and xb1are “101”. Those two X-coordinate values xb1 and xb1 are supplemented tothe coordinate tree in form of coordinate values constituting a frame inwhich a rectangular component is hollowed out by a triangular component.

This procedure explained referring to FIG. 7 to FIG. 13 is executed onthe Y-coordinate value yb2 shown in FIG. 6 too, and as shown in FIG. 14,merging of the coordinate trees is completed.

Incidentally, according to the above-mentioned explanation, there is noexplanation as to a case where sides, which constitute each of aplurality of components constituting an image, intersect each other. Incase of intersection of the sides, however, when the coordinate tree ismerged, the intersection point of those sides is also computed. Thosesides are divided at the intersection point and a new set of upper sidepoint and lower side point is established. Further, a horizontal linepassing through the intersection point suitably divides the image.

The creation and merging of the coordinate trees in the step S01 to thestep S04 are repeated for each of the components constituting the image(a step S05 in FIG. 1). As a result, it is possible to obtain acoordinate tree in which all of the coordinate trees of the componentsconstituting the image are merged. Thus, area data representative of anarea in which an image is divided is created from the merged coordinatetree (a step S06 in FIG. 1).

FIG. 15 is a view showing area data generated from coordinate trees.

Area data representative of polygonal area consisting of combinations ofthe upper and lower side lines and the horizontal lines are sequentiallyextracted from the upward stream side of the coordinate trees shown inFIG. 14. Here, total five area data 330 are extracted. Extraction ofthose area data 330 causes the image shown in FIG. 2 to be substantiallydivided into five areas. Appended to the extracted area data are areanumbers “103”, “104”, “105”, “106” and “107”, which are for distinguishthe areas represented by the area data from one another.

FIG. 16 is a view showing a divided image.

FIG. 16 shows a result that the image shown in FIG. 2 is divided intofive areas such as the area numbers “103”, “104”, “105”, “106” and“107”. Horizontal lines 211 passing through vertexes B1, B2 and B3divide the image. According to the present embodiment, all thehorizontal lines passing through vertexes B1, B2 and B3 unconditionallydivide the image.

Next, an area number table representative of a positional relation amongthe areas is created in accordance with the area data extracted from thecoordinate trees and then created (a step S07).

TABLE 1 Area Nos. on Area Nos. on Area Nos. on Area Nos. upper rightbelow 103 non non 104, 105, 106 104 103 105 107 105 103 106 107 106 103non 107 107 104, 105, 106 non non

Table 1 shows an area number table created in accordance with the fivearea data 330 shown in FIG. 15. An area number column of the left end ofthe area number table shows numbers of areas represented by the areadata 330 shown in FIG. 15. Three columns of right side of the areanumber table show numbers of areas adjacent upward, rightward anddownward with respect to the areas represented by the numbers shown inthe area number column, respectively. Here, the areas adjacent upwardand downward are areas adjacent upward and downward with respect to thehorizontal line, respectively. The area adjacent rightward is an areaadjacent rightward with respect to the upper and lower line. Withrespect to the area of the number “105”, it is processed assuming thatthe horizontal line of the length “0” interposed between two upper sidepoints exists at the position of the vertex against the base of thetriangle.

Area information represented by the respective stage of the area numbertable thus created denotes a positional relation between a certain areaand a peripheral area of the certain area. The area information isderived from the area number table one by one for a stage of areainformation (a step S08 in FIG. 1), and it is determined as to whetherthere is a plurality of areas adjacent upward or downward with respectto a certain area (a step S09 in FIG. 1). For example, according to thearea number table shown in Table 1, three areas exist downward the areaof the number “103”, and three areas exist upward the area of the number“107”.

Thus, in the event that there is a plurality of areas adjacent upward ordownward, the area is further divided by a vertical line extending in avertical direction (a step S10 in FIG. 1). In the area number tableshown in Table 1, the area of the number “103” and the area of thenumber “107” are an object of the further division, and as will bedescribed, they are divided by the vertical line.

The above-mentioned processing of the step S08 and the step S09 isrepeated on the whole area information shown in the area number table (astep S11 in FIG. 1).

FIG. 17 is a view showing an image in which an area is divided.

The area of the number “103” shown in FIG. 16 is divided into threeareas by a vertical line 212 passing through the vertex B1. Appended tothose three areas are area numbers “103”, “108” and “111”. It is notedthat the area of the number “111” is “0” in area. The area of the number“107” shown in FIG. 16 is divided into three areas by vertical lines 212passing through the vertexes B2 and B3. Appended to those three areasare area numbers “107”, “109” and “110”. According to the presentembodiment, of the vertical lines passing through the vertexes, thenecessary minimum of vertical line is selected and is used for adivision.

After such a division of the areas is performed, the area number tableis remade.

TABLE 2 Area Nos. on Area Nos. on Area Nos. on Area Nos. upper rightbelow 103 Non 111 104 104 103 105 107 105 111 106 109 106 108 non 110107 104 109 non 108 non non 106 109 105 110 non 110 106 non non 111 non108 105

Table 2 shows one in which the area numbers table shown in Table 1 isremade after the further division of the areas. As a result of thefurther division of the areas, the association between the areasmutually adjacent in the upper and lower direction is given by aone-to-one correspondence.

Color information representative of colors of areas represented by thearea numbers shown in the area number table thus remade is obtained inaccordance with the component data and is supplemented to the areanumber table a step S12 in FIG. 1).

TABLE 3 Area Area Nos. on Area Nos. on Nos. Colors upper Colors rightColors 103 Magenta non 111 Magenta 104 Magenta 103 Magenta 105 Cyan 105Cyan 111 Magenta 106 Magenta 106 Magenta 108 Magenta Non 107 Magenta 104Magenta 109 Magenta 108 Magenta non non 109 Magenta 105 Cyan 110 Magenta110 Magenta 106 Magenta non 111 Magenta non 108 Magenta

Table 3 shows an area number table in which the color informationrepresentative of colors of areas represented by the area numbers shownin Table 2 is supplemented. Color information representative of cyan iscombined with the area number “105”, and color informationrepresentative of magenta is combined with other than the area number“105”.

A trapping candidate to be subjected to trapping is determined inaccordance with the area number table to which the above-mentioned colorinformation is supplemented, and a predetermined trapping condition, inform of an area pair (a step S13 in FIG. 1). For each of the stages inTable 3, it is checked as to whether a pair of an area represented bythe area number shown in the area number column and an area adjacentupward the area (first occurrence) satisfies the trapping condition.Further it is also checked as to whether a pair of an area representedby the area number shown in the area number column and an area adjacentrightward the area (first occurrence) satisfies the trapping condition.According to the present embodiment, as colors of areas, only two colorsof magenta and cyan are supposed. Accordingly, there is used such asimple trapping condition that the trapping is performed when colors ofthe adjacent two areas are different from each other.

TABLE 4 Object areas Colors Trapping Object Colors 104 Magenta 105 Cyan105 Cyan 106 Magenta 105 Cyan 111 Magenta 109 Magenta 105 Cyan

Table 4 shows area pairs satisfying the above-mentioned simple trappingcondition.

As a trapping condition other than the above-mentioned simple trappingcondition, there are considered, for example, such a condition that atrapping is performed when a color difference between the mutuallyadjacent two areas is larger than a predetermined color difference, andsuch a condition that a trapping is performed when a difference inchromaticity between those two areas is larger than a predeterminedvalue.

When the area pair as shown in Table 4 is determined, the trapping areais created in accordance with the following procedure.

First, a pair of areas as a trapping candidate is obtained (a step S14in FIG. 1). Then, a band-shaped trapping area, which extends along theboundary of two areas constituting the area pair, is created (a step S15in FIG. 1). As a position at which a trapping area is created, there areconsidered three ways of one side, another side and both sides of theboundary line of two areas adjacent to each other. Here, a trapping areais created in a condition that the trapping area is created always atone side of the magenta side. As a technique of creating a trappingarea, here, there is adopted such a technique that a segment extendingin parallel to the boundary line is determined, and a band-shaped areainterposed between the segment and the boundary line is created in formof a trapping area.

As a color applied to the trapping area thus generated, there areconsidered the same color as a color of one of the two areas and neutraltints of colors of the areas. Here, the neutral tints of cyan andmagenta are applied to the trapping area.

Generally, there is generated a trapping area according to the colordifference between two areas mutually adjacent. For example, in theevent that the color difference is large, there is created a trappingarea in which an area light in color makes inroads into an area dark incolor. In the event that the color difference is small, there is createda trapping area in which both the areas make inroads into one another.

FIG. 18 is a view showing a created trapping area.

According to the present embodiment, a segment extending in parallel tothe boundary line is determined assuming that the boundary line istranslated in parallel to any direction of four directions of the upperand lower sides and the right and left sides by a predetermined amountw. In FIG. 18, a pair of an area of a number “104” and an area of anumber “105” is a trapping candidate. A boundary line 221 of those areasis subjected to a parallel translation horizontally in the leftdirection of the figure, so that a segment 222 having two coordinatepoints (xb1-w, yb1), (xb2-w, yb2) as its both ends is determined. And anarea hatched, which is interposed between the segment 222 and theboundary line 221, is created in form of a trapping area 223.

The above-mentioned step S14 and step S15 are repeated until all of thearea pairs as the trapping candidates as shown in the Table 4 areobtained and trapping areas for all the area pairs are created (a stepS16 in FIG. 1: Yes).

FIG. 19 is a view showing a state that trapping areas are created on allthe area pairs shown in Table 4.

There are created three band-shaped trapping areas 223 in such a mannerthat the areas 223 encircle a triangular area of the center. Further,there is also created a trapping area 223 of an area “0” upward thevertex opposing to the bottom of the triangle.

The trapping areas thus created are combined so that an integratedtrapping area is created (a step S17 in FIG. 1)

FIG. 20 to FIG. 23 is views showing the procedure in which an integratedtrapping area is created in the step S17.

Hereinafter, there will be explained the procedure in which anintegrated trapping area is created, referring to the figures.

FIG. 20 shows vertexes of a polygonal, which constitute the trappingareas 223 created in the step S14 to S16, together with coordinatevalues of the vertexes. A coordinate tree 340 shown in FIG. 21 iscreated in accordance with the coordinate values of the vertexes. Asshown in FIG. 22 with hatching, coordinate values 341 of external pointsconstituting an external form of the integrated trapping area areextracted from the coordinate tree 340.

Thereafter, as shown in FIG. 23, an external form of line 232 is createdin such a manner that the external points 231 represented by theextracted coordinate values are sequentially coupled, and an integratedtrapping area 233, which is interposed between the external form of line232 and the above-mentioned boundary line, is created as shown withhatching.

According to the above-mentioned trapping area creating method, thenumber of divisions of an image is not many and an amount of arithmeticoperation is also not much. Thus, it is possible to create the trappingareas at high speed.

The number of divisions of an image and a divisional condition fordetermining as to whether an image is to be divided (for example, acondition for determining as to whether a division by the vertical lineis to be performed) are not restricted to the present embodiment and canbe suitably altered. Even if the number of divisions is increased as aresult that the divisional condition, which is different from that inthe present embodiment, is adopted, the total number of the divisions isrestricted to the number sufficiently not so many, and thus it ispossible to create the trapping area at high speed.

Further, according to the present embodiment as mentioned above, as anexample of the technique of dividing an image, there is shown thetechnique of the division by merging of coordinate trees. However, inthe division step of the present invention, it is acceptable that animage is divided in accordance with a technique other than the techniqueshown in the present embodiment as mentioned above.

As to a direction in which an area adjacent to a certain area is checkedin order to determine a trapping candidate, there are considered twoways of down and left, and two ways of up and left, other than two waysof up and right as mentioned above. Further, as to a divisionaldirection of an image, there are considered a 45-degree direction and a135-degree direction. In the event that such a divisional direction isadopted, as a direction in which the adjacent area is checked, there areconsidered two ways of upper right and lower right.

Finally, there will be described an embodiment of a trapping areacreating apparatus of the present invention and an embodiment of atrapping area creating program storage medium of the preset invention.

FIG. 24 is a perspective view of a trapping area creating apparatusaccording to an embodiment of the present invention. FIG. 25 is ahardware structural view of a trapping area creating apparatus accordingto an embodiment of the present invention.

A trapping area creating apparatus 400 is constituted of a computer.

The trapping area creating apparatus 400 comprises, on an externalappearance, a main frame unit 410, an image display unit 420 fordisplaying an image on a display screen 420 a in accordance with aninstruction from the main frame unit 410, a keyboard 430 for inputtingvarious sorts of information to the main frame unit 410 in accordancewith a key operation, and a mouse 440 for inputting an instructionaccording to, for example, an icon and the like, through designation ofan optional position on the display screen 420 a, the icon and the likebeing displayed on the position on the display screen 420 a. The mainframe unit 410 has a floppy disk mounting slot 410 a for mounting afloppy disk, and a CD-ROM mounting slot 410 b for mounting a CD-ROM.

The main frame unit 410 comprises, as shown in FIG. 25, a CPU 411 forexecuting a various types of program, a main memory 412 in which aprogram stored in a hard disk unit 413 is read out and developed forexecution by the CPU 411, the hard disk unit 413 for saving varioustypes of programs and data, an FD drive 414 for accessing a floppy disk510 mounted thereon, and a CD-ROM drive 415 for accessing a CD-ROM 520mounted thereon. These various types of elements are connected via a bus416 to the image display unit 420, the keyboard 430 and the mouse 440.

The CD-ROM 520 stores therein a trapping area creating program forcausing the computer to operate as a trapping area producing apparatus.The CD-ROM 520 is mounted on the CD-ROM drive 415 so that the trappingarea creating program, which is stored in the CD-ROM 520, is up-loadedon the computer and is stored in the hard disk unit 413. The trappingarea creating program thus up-loaded is developed on the main memory 412and is executed in the CPU 411.

When the CD-ROM 520 stores an embodiment of a trapping area creatingprogram of the present invention, the CD-ROM 520 corresponds to anembodiment of a trapping area creating program storage medium of thepresent invention. When the trapping area creating program is up-loadedand is stored in the hard disk unit 413, the hard disk unit 413, whichstores therein the trapping area creating program, also corresponds toan embodiment of a trapping area creating program storage medium of thepresent invention. Further, when the trapping area creating program isdown-loaded on the floppy disk 510, the floppy disk 510, which storestherein the trapping area creating program, also corresponds to anembodiment of a trapping area creating program storage medium of thepresent invention.

When an embodiment of a trapping area creating program of the presentinvention is up-loaded and executed as mentioned above, the trappingarea creating apparatus 400, which operates as an embodiment of atrapping area creating apparatus of the present invention, isimplemented. Here, an operation of the trapping area creating apparatus400 is an operation that the above-mentioned trapping area creatingmethod is executed.

FIG. 26 is a view showing an embodiment of a trapping area creatingprogram and a trapping area creating program storage medium of thepresent invention.

A storage medium 550 shown in FIG. 26 represents the floppy disk 510,the CD-ROM 520 and the hard disk unit 413 as shown in FIG. 25. Thestorage medium 550 stores therein a trapping area creating program 551including a division step 552, a decision step 553 and a trapping areacreating step 554.

The division step 552 causes the computer to execute the operation shownin the step S01 to the step S11 in FIG. 1.

The decision step 553 causes the computer to execute the operation shownin the step S13 in FIG. 1.

The trapping area creating step 554 causes the computer to execute theoperation shown in the step S14 to the step S17 in FIG. 1.

When the trapping area creating program 551 is up-loaded on the computerand is executed, the computer can create a trapping area at high speedin accordance with the above-mentioned trapping area creating method.

As mentioned above, according to the present invention, it is possibleto create a trapping area at high speed.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by thoseembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

1. A trapping area creating method comprising: dividing an image,represented by a combination of polygons to which colors are applied,into a plurality of image areas by at least one straight line passingthrough at least one vertex of the polygons, wherein an image area isdesignated by said at least one straight line and the boundaries of apolygon divided by said at least one straight line; determining iftrapping should be applied to each pair of image areas adjacent to oneanother in at least one direction of two predetermined directions; andcreating a band-shaped trapping area extending along a boundary of twoimage areas comprising a pair of image areas determined as beingsuitable for trapping.
 2. A trapping area creating method according toclaim 1, wherein said dividing the image uses straight lines extendingin same directions as said two predetermined directions passing throughthe vertexes of the polygon, and sides of the polygon.
 3. A trappingarea creating method according to claim 1, wherein said determinationuses, as said two predetermined directions, an upper and lower directionand a right and left direction of the image.
 4. A trapping area creatingmethod according to claim 1, wherein said determination is based on adifference between colors of two image areas constituting said pair ofimage areas.
 5. A trapping area creating method according to claim 1,wherein creation of said trapping area creates, as said trapping area,an area interposed between a line constituting said boundary and a lineobtained when said line (first occurring) is subjected to a paralleltranslation.
 6. A trapping area creating apparatus for creating atrapping area in accordance with a trapping area creating method, saidmethod comprising: dividing an image represented by a combination ofpolygons to which colors are applied, into a plurality of image areas byat least one straight line passing through at least one vertex of thepolygons, wherein an image area is designated by said at least onestraight line and the boundaries of a polygon divided by said at leastone straight line; determining if trapping should be applied to eachpair of image areas adjacent to one another in at least one direction oftwo predetermined directions; and creating a band-shaped trapping areaextending along a boundary of two image areas comprising a pair of imageareas determined as being suitable for trapping.
 7. A trapping areacreating program storage medium storing a trapping area creatingprogram, which causes a computer to execute a trapping area creatingmethod, said method comprising: dividing an image, represented by acombination of polygons to which colors are applied, into a plurality ofimage areas by at least one straight line passing through at least onevertex of the polygons, wherein an image area is designated by said atleast one straight line and the boundaries of a polygon divided by saidat least one straight line; determining if trapping should be applied toeach pair of image areas adjacent to one another in at least onedirection of two predetermined directions; and creating a band-shapedtrapping area extending along a boundary of two image areas comprising apair of image areas determined as being suitable for trapping, when saidtrapping area creating program is incorporated into said computer.